The present invention relates to sealing means for fusion-bonding an overlapped part of a wrapping material by using an ultrasonic vibrator which utilizes an oscillator and circuit resonance, more particularly to a method and apparatus for controlling a sealing temperature according to changes in thickness and properties of the wrapping material.
When there are changes in the thickness and properties of a wrapping material to be ultrasonically fusion-bonded, suitable bonding results cannot be achieved if heat generation is not commensurate with the thickness and material properties of the wrapping material, so that an ordinary ultrasonic sealing apparatus comprises means for manually adjusting the generated temperature by changing its frequency in order to deal with the changes in thickness and properties of the material. However, from a microscopic viewpoint, overall thickness of a wrapping material is not uniform due to processing errors, and there are also localized irregularities of properties in the wrapping material. It is thus physically impossible to properly manipulate the above-mentioned manual temperature adjustment apparatus relative irregularities of thickness and properties of the wrapping material which is moving at a fixed speed, posing a problem that fusion-bond irregularities appear in the wrapping material.
Accordingly, the present invention provides, as a method for fusion-bonding a wrapping material at a suitable temperature, a method for controlling fusion-bonding temperature of a wrapping material, comprising the steps of: in ultrasonic sealing means comprising a wrapping material and a sealing hammer that are in relative motion, an ultrasonic vibrator which actuates the sealing hammer and applies an impact to the wrapping material via the sealing hammer, and an electric circuit for applying oscillating power to the ultrasonic vibrator; measuring by a non-contact-type temperature sensor, in the vicinity of the sealing hammer, the fusion-bonding temperature of the wrapping material which is heated by continuous impacts of the sealing hammer; sending, to a variable-voltage device interposed in the electric circuit, output signals corresponding to measured temperatures being successively inputted to a control unit from the temperature sensor; and controlling, with the variable-voltage device, an amplitude of the moveable hammer in accordance with the measured temperature value, so as to make uniform the heating temperature of the wrapping material.
Further, an apparatus for implementing the above-mentioned method comprises: in which ultrasonic sealing means comprises a wrapping material and a sealing hammer that are in relative motion, an ultrasonic vibrator which actuates the sealing hammer and applies an impact to the wrapping material via the sealing hammer, and an electric circuit for applying oscillating power to the ultrasonic vibrator; a non-contact-type temperature sensor for measuring, in the vicinity of the sealing hammer, the fusion-bonding temperature of the wrapping material which is heated by continuous impacts of the sealing hammer; a control unit for continuously computing output signals for control corresponding to the temperature values measured by the temperature sensor; and means for sending output signals from the control unit to a variable-voltage device interposed in the electric circuit, and controlling an amplitude of the moveable hammer with the variable-voltage device, so as to make uniform the heating temperature of the wrapping material.
According to a conventional constitution, when the moveable hammer has a fixed amplitude, as the thickness of a wrapping material changes, the impact force on the wrapping material also changes, so that there arises a change in generated temperature. In addition, when there are irregularities in material properties of the wrapping material, the generated temperature changes in accordance with the irregularities thereof, so that the wrapping material cannot be fusion-bonded with uniform strength. However, according to the above-mentioned constitution, the generated temperature of a wrapping material is monitored and the amplitude of a moveable hammer is controlled so as to make the generated temperature uniform.